Hello Guo Ren,
On Thu, Dec 21, 2023 at 10:46:58AM -0500, guoren@xxxxxxxxxx wrote:
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> In COMPAT mode, the STACK_TOP is 0x80000000, but the TASK_SIZE is
> 0x7fff000. When the user stack is upon 0x7fff000, it will cause a user
> segment fault. Sometimes, it would cause boot failure when the whole
> rootfs is rv32.
Checking if I get the scenario:
In pgtable.h:
#ifdef CONFIG_64BIT
#define TASK_SIZE_64 (PGDIR_SIZE * PTRS_PER_PGD / 2)
#define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
#ifdef CONFIG_COMPAT
#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
#define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
TASK_SIZE_32 : TASK_SIZE_64)
#else
[...]
Meaning CONFIG_COMPAT is only available in CONFIG_64BIT, and TASK_SIZE in
compat mode is either TASK_SIZE_32 or TASK_SIZE_64 depending on the thread_flag.
from processor.h:
#ifdef CONFIG_64BIT
#define DEFAULT_MAP_WINDOW (UL(1) << (MMAP_VA_BITS - 1))
#define STACK_TOP_MAX TASK_SIZE_64
[...]
#define STACK_TOP DEFAULT_MAP_WINDOW
where:
#define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
with MMAP_VA_BITS_64 being either 48 or 37.
In compat mode,
STACK_TOP = 1 << (32 - 1) -> 0x80000000
TASK_SIZE = 0x8000000 - 4k -> 0x7ffff000
IIUC, your suggestion is to make TASK_SIZE = STACK_TOP in compat mode only.
Then why not:
#ifdef CONFIG_COMPAT
#define TASK_SIZE_32 STACK_TOP
With some comments explaining why there is no need to reserve a PAGE_SIZE
in the TASK_SIZE_32.
Does that make sense?
Thanks!
Leo
>
> Freeing unused kernel image (initmem) memory: 2236K
> Run /sbin/init as init process
> Starting init: /sbin/init exists but couldn't execute it (error -14)
> Run /etc/init as init process
> ...
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: add2cc6b6515 ("RISC-V: mm: Restrict address space for sv39,sv48,sv57")
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> ---
> arch/riscv/include/asm/pgtable.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index ab00235b018f..74ffb2178f54 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -881,7 +881,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> #define TASK_SIZE_MIN (PGDIR_SIZE_L3 * PTRS_PER_PGD / 2)
>
> #ifdef CONFIG_COMPAT
> -#define TASK_SIZE_32 (_AC(0x80000000, UL) - PAGE_SIZE)
> +#define TASK_SIZE_32 (_AC(0x80000000, UL))
> #define TASK_SIZE (test_thread_flag(TIF_32BIT) ? \
> TASK_SIZE_32 : TASK_SIZE_64)
> #else
> --
> 2.40.1
>
